1. Technical Field
The present invention relates to a sensor device, a sensor module, a force sensing apparatus, and a robot.
2. Related Art
In the related art, a force sensor disclosed in JP-A-4-231827 is known as a force sensor used with piezoelectric materials. The disclosed force sensor has a configuration in which a signal electrode 15 shown in FIG. 15 of JP-A-4-231827 is interposed between crystalline circular plates 16 which are piezoelectric materials, and a plurality of measuring elements which are interposed between metal cover circular plates 17 are disposed in a metal ring 14 by welding as shown in FIG. 4 of JP-A-4-231827.
FIG. 14 shows a sensor device of the related art. As shown in FIG. 14, a sensor device 200 includes a sensor element 214, a metallic package 202 including a recess accommodating the sensor element 214, a metallic plate-like lid 204 which is joined to an upper surface (joint surface 224) which is an outer periphery of an opening portion 220 of the recess of the package 202 and comes in contact with the sensor element 214.
In the sensor element 214, a sensing electrode 218 is interposed between two opposed crystal plates 216 having the same cut surface with the sensor element. The upper surface of the crystal plate 216 is a force receiving surface 222 of the sensor element 214, and comes in contact with the lid 204.
Meanwhile, a coaxial connector 206 is attached to the side surface of the package 202. The coaxial connector 206 includes an outer periphery portion 208 and a center conductor 210, an insulating resin 212 is filled therebetween, and the outer periphery portion 208 and the center conductor 210 are electrically insulated from each other. Herein, the outer periphery portion 208 is short-circuited with the package 202 and the lid 204, and the center conductor 210 is electrically connected to the sensing electrode 218.
The sensor device 200 is interposed between pressurization plates (not shown) to receive pressure, and the lid 204 transfers a force (pressure) to the force receiving surface 222 of the sensor element 214. Then, the crystal plates 216 output (induce) an electric charge to the sensing electrode 218 by a piezoelectric effect caused by the pressurization. A force (pressure) to be applied to the crystal plates 216 changes according to an external force to be applied to the pressurization plates. Accordingly, it is possible to sense an external force applied to the sensor device 200 by monitoring an amount of change in an output electric charge due to the change of the force (pressure) through the coaxial connector 206, with an output of the signal in a case of only the pressurization as a reference.
Herein, in the sensor device 200, the sensor element 214 is sealed by the lid 204 in a state where the inside of the package 202 is full of dry air, so that the electric charge induced from the crystal plate 216 does not leak to the external portion by moisture or the like.
The force sensor disclosed in JP-A-4-231827 has a structure in which a signal electrode is interposed between crystalline circular plates, and the crystalline circular plates are interposed between metallic cover circular plates. In a case of attaching this to a metallic ring by welding, the individual portions such as a signal electrode and the like have dimensional errors and it becomes a concavity and convexity of the welded portion, and there is a concern that gaps may be generated in welding. Accordingly, in a state of an adverse external environment such as high humidity, there is a concern that the electric charge may leak to the external portion by an infiltration of moisture to the sensor element, so that a stable measurement is difficult.
In the sensor device of the related art shown in FIG. 14, a height of the force receiving surface 222 of the sensor element 214 accommodated in the package 202 and a height of a joint surface 224 which is an outer periphery of the opening portion 220 of the recess of the package 202 do not coincide with each other, in some cases.
FIGS. 15A and 15B show schematic views in a case where a force is applied to the sensor device (height of force receiving surface<height of joint surface) of the related art. FIG. 15A shows a schematic view before applying a force to the lid, and FIG. 15B shows a schematic view after applying the force to the lid. As shown in FIG. 15A, in a case where the height of the force receiving surface 222 of the sensor element 214 is lower than the height of the joint surface 224, the lid 204 is joined to the package 202. Then, a gap 226 is formed without a contact of the lid 204 and the force receiving surface 222 of the sensor element 214.
FIGS. 16A to 16C show schematic views of the sensor device (height of force receiving surface>height of joint surface) of the related art. FIG. 16A shows a schematic view before joining to the lid, FIG. 16B shows a schematic view after joining to the lid and before applying a force to the lid, and FIG. 16C shows a schematic view after applying the force to the lid.
As shown in FIG. 16A, in a case where the height of the force receiving surface 222 of the sensor element 214 is higher than the height of the joint surface 224 of the package 202, when the lid 204 is joined to the package 202, the state shown in FIG. 16B is realized. That is, the center portion of the lid 204 is raised, and a peripheral edge of the force receiving surface 222 of the sensor element 214 comes in contact with the lid 204, however, a gap 228 is formed between the center portion of the force receiving surface 222 of the sensor element 214 and the lid 204.
In all cases, when the force (including the pressurization described above) is applied to the lid 204, the gaps 226 and 228 described above are eliminated. However, as shown in FIG. 15B, a region which is on the outer side with respect to the sensor element 214 of the lid 204 and on the inner side with respect to edge of the opening portion 220 in a plan view when seen in a depth direction of the recess of the package 202, receives stress in a direction (direction of arrow 230) toward to the center of the lid 204. As shown in FIG. 16C, the region which is on the outer side with respect to the sensor element 214 of the lid 204 and on the inner side with respect to the edge of the opening portion 220 in a plan view, receives stress in a direction (direction of arrow 232) radiating from the center of the lid 204. Accordingly, in any of the cases, shear stress (a direction of arrow 234 is a direction of stress) is concentrically applied to the inner edge portion of the sensor element side which is the inner side of the joint portion (joint surface 224) obtained by joining the lid 204 and the package 202. Further, in the sensor device 200 to which a force is repeatedly applied, there is a concern that stress concentration may progress in the inner edge portion of the sensor element side of the joint portion, and the joint of the lid 204 and the package 202 may be degraded so as to break the air-tight seal.